The invention relates to a suction box for stabilizing a web at a connection or splice position at which a new web is attached to a previous web, at a location upstream of a threading point where the web is threaded onto a roll. While use of this apparatus in a web coater is described, the apparatus has use in other applications.
In a coater for one or both sides of a web of paper, when one roll or supply of paper is exhausted and another roll or supply of paper is substituted, the trailing end of the exhausted roll and the leading end of the new roll must be spliced. Only a flying splice at full operating speed, which may be on the order of 1,500 m./min., guarantees high efficiency and best production rate. To accomplish this, both the old supply or roll of the web and the new supply or roll of the web to be coated must be delivering web the same speed, that is the web must be coming at the same speed. The old web must be severed cleanly to develop a tail to which the leading end of the new web might be spliced, and short effective splices between the two webs are needed.
For an effective splice, the trailing end of the recently cut web must be kept stable, and means are typically provided for achieving web stabilization. These means include the use of a suction generating means, such as a suction box, over which the web moves and which holds the web stable as it moves past. An example of an unwinding unit of an off-line coater in which the present invention might be used is shown in an informative brochure of the assignee hereof, namely Voith Brochure p2579e. Web stabilization through use of vacuum is known, as shown in U.S. Pat. No. 4,502,231.
For web stabilization, so called foils are also used on web splice equipment for connecting the ends of two webs, i.e. the foils are used with the suction boxes. The suction box stabilizes the web run by means of the vacuum in the box and by the surface of the box facing the web over which the web runs. In restricted space conditions, like that in the area of the pressure roll on its upstream side toward the new paper roll, the large distance between the slot point or nip of the pressure roll and the end of the suction box still causes web flutter. Such flutter results in crushing of the web and improper bonding of the old web to the new or else, in particular, it causes difficulties with later processes performed on the web, for example, in a succeeding coating unit.